Transcutaneous Electrical Nerve Stimulation (TENS) devices apply electrical currents to a particular area of the human body in order to suppress pain. The most common form of TENS is commonly referred to as “conventional TENS”. In conventional TENS, electrodes are placed on the user's skin within, or adjacent to, or proximal to, the area of pain. An electrical circuit generates stimulation pulses with specified characteristics. One or more pairs of electrodes, placed on the user's skin, transduce the electrical pulses and thereby stimulate underlying nerves in order to relieve pain. TENS electrodes typically utilize hydrogels to create a stable low-impedance electrode-skin interface to facilitate the delivery of electrical current to the user so as to stimulate peripheral sensory nerves. Close contact of the electrode (both gel pads and backing materials) with the skin of the user creates a temporary barrier that limits the covered skin area from being exposed to the air.
Pain relief from TENS stimulation usually begins within 15 minutes of the stimulation onset and may last up to an hour following the completion of the stimulation period (also known as a “therapy session”). Each therapy session typically runs for 30-60 minutes. To maintain pain relief (i.e., hypoalgesia), TENS therapy sessions typically need to be initiated at regular intervals. Newly developed wearable TENS devices such as the QUELL™ system developed by Neurometrix, Inc. of Waltham, Mass., USA provide users with an option to automatically restart therapy sessions at pre-determined time intervals.
The convenience of “wear-and-forget” TENS technology may lead some users to wear the TENS device for an extended period of time without removing the device from the contacted skin area. Covering the skin area with a TENS device for an extended period of time may cause skin irritation for the user. It is therefore important to monitor the “on-skin” time duration of the TENS device and, where the “on-skin” time duration exceeds a limit, to provide the user with feedback and a reminder (prompt) to “air-out” the skin under the device (i.e., by temporarily removing the TENS device from the user's skin).